Ratio control of binder to concentrate



A. s. HENDERSON ETAL 2,909,303

RATIO CONTROL OF BINDER TO CONCENTRATE 5 Sheets-Sheet 1 Oct. 20, 1959Filed Dec. 9, 195"! INVENTORS.

CmmaLL D. Ca es: BY J'ahw I'P. R1505 Oct. 20, 1959 A.S.HENDERSON ETALRATIO CONTROL OF BINDER T0 CONCENTRATE 5 Sheets-Sheet 2 Filed DeC. 9,1957.

Oct. 20', 1959 A. S. HENDERSQN ET AL RATIO CONTROL OF BINDER TOCONCENTRATE Filed Dec. 9, 1957 5 Sheets-Sheet 3 '4, HLIIVG N0 m1. 0.C4055 y 50H 17. 01:04

AVTTOIPNE'YJ Oct. 20, 1959 A. s. HENDERSON ETAL 2,909,303

RATIO CONTROL 6F BINDER T0 CONCENTRATE Filed Dec. 9, 1957 5 Sheets-Sheet4 Oct. 20, 1959 A. s. HENDERSON ETAI. 2,909,303

RATIO CONTROL OF BINDER TO CONCENTRATE Filed Dec. 9, 1957 5 Sheets-Sheet5 .ening or induration step.

I pellets.

RATI O CONTROL OF BINDER T CONCENTRATE Ashland S. Henderson and CarrollD. Cross, Silver Bay,

and John R. Riede, White Bear'Lake, Minn., assignors to Reserve MiningCompany, Silver Bay, Minn., a corporation of Minnesota ApplicationDecember 9, 1957, Serial No. 701,673

11 Claims. (Cl. 222- 57) This invention relates to novel and improvedmethods and means for automatically controlling the amount of a bindermaterial to be added? to a base materialwhich has magneticcharacteristics It is particularly adapted to the automatic control ofthe amount of a binder material to be added to a comminuted mass of orehaving a substantial proportion of magnetic oxide of iron therein. As aconvenient example of one advantageous adaptation 'of the invention itwillbe described in connection with the operation of pelletizingbeneficiatedtaconite concentrate.

lets of such concentrate they are indurated' by'heating and burning, ina continuous process, such as in a moving grate furnace or a stackfurnace. During'theforination'of the pellets prior to induration it hasbeen found advisable to add a small proportion of a binder material,such as bentonite or starch, to the concentrate powder so as to promoteadhesion of the particles while they are being formed into pellets, andfurther maintain the shape of these pellets during the step of conveyingthem to and through the induration furnace. concentrate, mixed with thedesired amount of binder, is fed to a large hollow drum whichis'rotating on a slightly inclined axis, with the m'oist concentratepowder turning over and over on the inner drum wall while simultanemotor'28; Here again it is apparent that by varying The powdered ouslyprogressing towards the discharge end of the drum. w

The ore'particles agglomerate' by snowballing into spherical particlesranging in size from one quarter inch of the drum, the percentage ofbinder material, and'other factors, the production of spherical orapproximately spherical balls or compacts may be satisfactorilyaccomplished. When properly made the .pellets are strong enough to holdtheir shape preparatory to the heat hard- From what has been said itwill be apparent that the feed. of concentrate and binding materialmustbe controlled so as to produce green pellets of proper adhesivecharacteristics. If too much binder is neededit is economic'allyundesirable by reason of thecost ofthe binder, and it reduces to a minorextent the iron content of the If insufficient binder is used, thenbreakage 'of pellets increases in the subsequent handling, besides whichthe pellets do not form as readily' in the ballingdrum.

The primary object of the invention is to control the amount of magneticiron con centrate fed to. the balling drum independent of its feedingcharacteristics, while simultaneously addin'g'to the concentratepowder'apredetermined weight of binder to the concentrate so. 'as" toachieve the proper ratio of the two ingredients.

A further object of the invention is to maintain 'constant theconcentrate-binder ratio regardless of'varia tions in concentratequantity. r

A further object of the inyention is toprovide a uniform control circuit"which will correct for any changes in feeding characteristics of eitheringredient.

. 25' In the'final step of preparing balls, compacts or pel- 2,909,303Patented Oct. 20, 1959 of our invention the pellets are formed in aballing drum 20 fed by a continuous conveyor 21 which may be a slightlyconcaved or shallow trough belt. Belt 21 travels in the direction of thearrows, being driven at a preselected constant speed by motor 22.Concentrate powder, consisting in the present instance of beneficiatedtaconite ore having a high magnetic content, is discharged from a sourcesuch as bin 23 onto a variable speed table feeder 24 from which itdischarges to conveyor 21.

Table feeder 24 is energized by a variable speed motor '25. It will beunderstood that by suitable control of the current to motor 25 it ispossible to control the amount of concentrate delivered to conveyor 21by table feeder 24, l

V A suitable binder material, in finely ground form, is

' fed from ,a bin 26 to a table feeder 27, and discharged therefrom toconveyor 21 so as to travel with the concentrateto drum 20. Table feeder27 is operated by a the electrical input to motor 28 it is possible tovary the 'amount of binder delivered to conveyor 21.

Control of motors 25 and 28 will be briefly discussed here, and laterwill be described in detail in connection with the more detailed wiringdiagrams, Figs. 2 to 5.

Conveyor21 carrying the concentrate and binder passes in successionthrough three annular coils constituting an inductive couple consistingof a primary coil P disposed between a pair of appropriately connectedsecondary coils The primary is energized by any suitable source ofalternating or pulsating current applied at terminals L L Variations inthe amount of magnetic naterial passing axially through the primary coilproduces corresponding and proportional variations in an alternatingcurrent induced in the secondary coils S and S These secondaryvariations are imposed on a controller 29 through an amplifier 30. Onefunction of the controller is to regulate the speed of motor 25 througha circuit 31 to deliver a uniform amount of magnetic. concentrate toconveyor 21. Another functron of controller 29 is to send a signal to asecond controller 32 through a circuit 33. This second controller 32through a'circuit 34 controls the operation of motor 28, tomaintaintheratio of binder to concentrate in a predetermined proportion.

In addition'to their functions in the control operation ,ius'tdescribed, controllers 29 and 32 may be provided with indicating meansto respectively show, in actual weight units, theamount of concentrateand binder being delivered to the balling drum. The amount of magneticmaterial sensed by the primary-secondary inductive couple is also ameasure of the total weight of concentrate because the concentratecomposition isquite uniform, and a measure of its magnetic content givesa reliable indication of its total weight. The indicating means which 1sapart ofcontroller 29 can therefore be calibrated in tons-of'concentrateperunit of time.

'I'heind icatingmeans associated with, controller 32 trical outputproportionally. to variation in speed of mo- .feeder27. This feed-backsignal is-supplied to an indicator in controller .32. The indicator notonlyxcan be calibrated to read-in pounds of binder perunit of time, butit can be integrated with a signal from the concentrate controller 29 toshow the-simultaneous exact;ratio of concentrate to binder.

As a brief rsum, the inductive couple is sensitive to variations in theamount of magnetic'material in the conveyor burden. A first controller,in responseto a varying signal from the inductive couple, transmits a.proportionally varying current to the motor which controls the deliveryof concentrate so as to maintain the delivery as constant as ispracticable. Simultaneously this firstcontroller transmits a signal to-a second controller which regulates the binder feed. The binder feedsends back to the second controller a signal which can be integratedwith the signal from-the first controller to show, at any instant,thetexact ratio of concentrate to binder. Indicator means are providedto show the actual weight of concentrate and binder.

Referring now to the electricalcircuits and'members associated therewithwe show; in theupper left portion of Fig. 2, the sensing means forquantitatively determining the amount ofmagnetic concentrate moving in apath past the induction couple consisting of primary coil P, and twosecondary coils S and 5 which in a structural assembly are axiallyspaced one on each side of the primary. The conveyor 21 (Fig. 1) 'passesaxially through the couple, .and any magnetic material thereon increasesthe induced current in S S An A.C. current from L L feeds into aconstant voltage transformer 40 through a resistor -41 into primary P.One side is grounded at 42. The voltage developed in S S is proportionalto the quantity of magnetic concentrateon the conveyor.

The AC. current flowing in thesecondary circuit is rectified by diode 43so that'the D.C. voltagedrop across resistor 44 is proportional to theaforesaidamounts of magnetic material. It is necessary to makeanoperating correction for extraneous effects in the operating circuitother thanthose resulting from passage of the magnetic concentrate onthe conveyor. This correctionis efiected by taking part of thetransformer output through aphasing capacitance 45 and a variableresistor 46. .Inessence, the object is to vary resistor 46 to produceatdiode rectifier 48 a voltage equivalent to that at diode 43 when thecircuits are energized but no magnetic material is passing on theconveyor. Under'these conditions the DC. voltage across resistor. 44isequal and opposite to the DC. balancing voltage across resistor 49with no magnetic material. passing:

A variable resistor 52.and a coupled capacitor .53 act as a matchedresistance-capacitance circuit to dampen the signal developed by passageofmagnetic material. Re sistor '52 could be of fixed value, but forconvenience 'avariableresistor is provide'd to modify'thesignalvoltageat points 54, '55, so that'a signal of predetermined potential can'befedtothesubsequent circuit elements.

The signal'from'points54-,55 is shown in.iFig. .2 as being delivered insuccession to two'units, in'this drawing identifiedby'reference'numerals Sfiwand 30b. and coninpper'part of Fig.3constitutes-a balancing bridge of. the Wheatstone general type, in whichpoints 64, 61, 65, and

- (Fig. .2) which in turn operates several items, as will ap- .rts.checkmgposttton, during wh1ch movement a clutch its coming signal at.54, 55.

4 cell which, when used only as an occasional check means, remains atconstant valuefor a long period. We have provided a multiple throwswitch 58 which can be manually thrown to a check position at selectedintervals, but which normally is in the opposite or running position.

At the signal input point there is a resistor-capacitor alternatingcircuit consisting ofresistor 59 and a capacitor .60.. .Switch 58.. isin the upper .or normal operating position, which places'resistor'59inelectric circuit communication with-point 61 through lines'62 and 63.The

the intermediate resistors 66-and '67 form a lower arm, andpoints 64,68, .69, and 65, and the intermediate resistors 70, 71, and the parallelresistor assembly 72, 73 and 74 form the:upper.arm. Theintermediatecross arm 64, 75, '65 contains the battery 76 and a variable resistor77. In the parallel resistor bank 72, 73, 74, is a variable element50.for balancing purposes.

Battery 76 supplies a constant voltage between points 64. and .65. Thisvoltage is arranged to be of opposite polarity tothesignal beingmeasured. With the switch -still in,.the upperposition the incomingsignal to be measured-proceeds from point 54 through lines 62 and .6310point 6l, and from point 55 through the amplifier (connected atpoints 80and 81) and then through lines 82. and-83 to .point 5t). Signal voltageat the terminal points '61 and 50 therefore is disposed, by means of themeasuring bridge above described, to be opposed in polarity to thevoltage of battery 76. The amplifier (Fig. 4) in serieswith terminals80-and81 is connectedto measure and amplify any difference-between theestablished battery voltage and the fluctuations in the incoming signalat 54, 55, coming from theinduction couple heretofore described. Theamplified current energizes a motor .84

pear. 'It.may now be stated that one of its functions is to operate thesliding contact on resistor 74 (Fig. 3) to a position such that thevoltage'produced by battery 76 across points 61 and181 is equal andoppositeto the in- It is apparent that when the signal is thus'balancedthere will be no output signal at points -80.and-81, which will in turnleave-no potential to be amplified andconsequently motor 84 (Fig. 2)will stop. Motion of the motor to the stop position, however, will havemade the necessary adjustments .in the further controlled elements toachieve the results desired.

To assure a .proper balancing voltage output from bat- .tery 76 (Fig. 3)it is occasionally checked against astandard cell.85,-..as.follows.Manual switch 58 is moved to mechanism (not shown) simultaneouslyconnects the slider on..-re'sistor 77 with motor84 (Fig. 2).

With the switch .in the down or' check position the voltage originatingin battery 76 and developed across resistor 67 is compared with thevoltage of standard cell 85 and impressed between points'86 and 87.Since the signal voltage at terminals 54 and 55. has beendisconnected'by moving switch 68 to the check position, the

aniplifierwill now amplify a differential impressed, across resistor'88, the amplifier circuit proceeding from terminal "81 through lines82,90,-resistor'38, and lines 91 and 92 .to terminal 80. ..Any detectablepotential difference .thetwo'voltages equal and opposite. This willperiodically check and adjust. the.battery-voltage and insure accuratemeasuring' of "the incoming signal at 54, 55. Switch 58.islofrcoursereturmd to the upper or normal operatin po i stion aftereach check. 7 t

g .In thisimeasuring.circuit, Fig. '3, norreference'has as yet.beenlmadeJtoresistor"95. .This resistor, by-means of pellets.

resistor provides a potential drop arrangement which is used as a supplyof constant voltage, low wattage power for a retransmitting slidewireunit.

Proceeding from terminal points 80 and 81'of Fig. 3 We arrive at thesimilarly identified'terminal points at the left side of the amplifierdiagram, Fig. 4. This shows a fairly conventional'DC; amplifier whichtakes the low potential signal coming in at 80, 81 and amplifies itsufficiently to energize balancing motor 84 (Fig.2). As has been seen,the balancingmotor operates to return the energizing voltage to a zerovalue. As heretofore intimated, as long as the ,voltage atterminals 54,55 (Fig. 3) is constant no potential difference is detected at terminals80, 81. The position to which motor 84 moves to achieve thisbalance isthen representative of the signal impressed at the points 54, 55.

In Fig. 4 theunbalance of the measuring circuit is noted at terminalpoints 80 and 81 and is converted to alternating current by inputtransformer 99 and converter 100 and shaped by'the matchedresistor-capacitor elements 101 and 102. The alternating current signalis then fed to two 12AU7 tubes 103 and 104 in tandem amplifyingrelationship, and thereafter the output from tubes 103 and 104 isdeliveredto the grids of two 12AX7 tubes 105 and 106. The greatlyamplified signal isthen fed to one winding 84a of the split phase motor84 already mentioned (Fig. 2) the other winding 84b being energized fromlines L3 and L4 of a 110 volt A.C. supply. Power transformer 107 has aprimray 108 energized from lines L3, L4 with an optional adjustable tap108a. Various secondary taps provide voltages where needed, for exampletaps 109 and 110 supply plate potentials of approximately 275 volts forthe tubes 105 and 106, and taps 111 and 112 supply filament voltage fortubes 103 and 104. Since the amplifiers characteristics and and circuitswill be apparent to one skilled in the art, no further or more detaileddescription is necessary.

Summing up, at this point, the functions of motor 84, which responds toamplifier 30b shown in block outline in Fig. 2, and in circuit detail inFig. 4, the motor operates (a) the moving slider on battery rheostat 77(Fig. 3), (b) the sliding connector on rheostat 74 (Fig. 3), (c) aretransmitting slidewire connector on rheostat 113 (Fig. 2). Thelinkages for the operation of these controls are indicated in brokenlines on Fig. 2.

amount of binder is controlled so as to be fed to the balling drumconveyor 21 in proper proportion to the amount of magnetic concentratefed to the same conveyor.-

Referring again to Fig. 2, a signal comprising a potential drop fromterminal points 96 and 97 (Fig. 3) is applied at the similarly numberedpoints at the top right of Fig. 2 and is rendered eifective onretransmitting slide wire resistor 113 through dropping resistor 116 andlines 117 and .118 to two points ,11913111 120 of an electric bridge114. Two opposed points 121 and 122 on the same bridge receive, throughlines123, 124 and 12 5, a signal from tachometer generator 35. Thissignal passes through dropping resistor 126 and voltage divider 137, thesignal beingproportional to the coal being mixed with the Motor 84 isresponding to any variationsin the magnetic content of the concentrateand through the mechanit. 6 cal linkage with slide wire moving contact113;; the motor 84 varies the value of the constant voltage input at 96,97 so as to transmit to the electrical bridge 114 a current to bebalanceda'gainst the signal from generator 35. The resulting unbalancedstatus, if any, is transmitted through lines 124 and to amplifier 126.whereby to operate a motor 127. Motor 127 through mechanical linkage 128rotates to restorethe balanced status by movement of the contact at 121on the electric bridge, but also through another mechanical linkage 129moves the slider on a proportional resistor 130 electrically associatedwith a standard electroline relay 131 the operation of which will bedescribed in connection with Fig. 5.

Relay 131 operates motor 132 whichthrough mechanical linkage 133 movesthe sliding contact on potentiometer 134 which is in the fieldcircuit ofmotor 28 through lines 135 and 136. Motor 28 operates the table feeder27 which controls the binder feed from bin 26. V

It will be apparent that the signal from the primarysecondary couple,representing Variations in magnetic content of concentrate, has thusbeen integrated with the signal from the tachometer generator,representing the amount of binder being fed, and a predetermined ratiosetting, electrical bridge 114, exerts afeed back control on the speedof binder feedmotor 28. Putting it simply, if the pre-set equilibriumpoint of electrical bridge 114 is thrown out of balance byfiuctuationssignalled by the tachometer generator, then amplifier 126magnifies the fluctuations, motor 127 operates'to restore the balance,but concurrently motor 127 through relay 131 ,communicates the situationto motor 132, which lattermotor regulates the speedof table feeder motor28 to bring the binder feed to the desired value.

Still referring to Fig. 2, we show means for controlling the speed ofthe table feeder 24 for the concentrate feed. Motor 84 throughmechanical linkage moves the contact point of a proportioning resistor141 of another electroline relay 142 which in turn responsively operatesmotor 143. This motor 143 through its linkage 144 operates the movingcontact of a speed controlpotentiometer 145 in circuit with the field ofmotor 25. which operates the table feeder 24 for supplying concentrate.The hookup just described between motor 25 and motor 84 is arrangedappropriately to be sensitive to variations in concentrate feed, and torestore the unbalance sensed by measuring device 30a (Fig. 3) andamplified by, the amplifier 30b. Amplifier 30b and amplifier 126, aresimilar in structure and operation, as also are electroline relaydevices131 and 142 which willnow be briefly described in connection withFig. 5; I

The relay actually shown in Fig. 5 is a conventional type, one suchbeing obtainable from Minneapolis-Honeywell Regulator Company. Thepurpose of the relay, is to accept a signal received at 141 (Figs..2'and-5) and, responsive thereto, to deliver a current at terminals 146,147, to become effective on motor 143. This operation involves controlof proportionalband, reset, and approach rate functions which arefamiliar to those skilled;in1the motor control It is not necessary to gointo extended detail as'to the manner of operation of the electrolinerelay control of a modutrol motor beyond the brief characterization nowfollowing.

A signal entering at terminals 151 and 152 becomes effective, throughthe various proportional band resistors 153, 154, 155, 156, 157 upontube 158, the output of which is fed to tubes 159. There areinterrelatedmodifying effects produced by heaters Y160 and 161 inconjunction with electrical bridge 162, and the resultant signal isimposed on tubes 163 and 164. The ultimate effect, through the mediaofrelay coils 165 or 166 operates contacts 167 or 168 respectively, andconsequently controls the rotation of motor 22, in the case ofelectrolinfe relay 142. Relay 131 functions similarly. a 7

As we have explained hereinabove we have provided means for controllingthe feed of concentrate-and binder to a predetermined proportion, theproportion being maintained even' though the magnetic content of theconcentrate varies. If thegmagnetic content does vary, then theconcentrate feed isproperlyvaried to restorethe feed toa'predetermined'value, independent of its feeding characteristics, whilestill'keeping-the concentrate-binder ratio ,atthe proper value.

Either an indicating or a recording means can be electricallyor-mechanically associated with the several con- 'trols describedherein. The indicating means could be a 'pointer'on a dial. .Therecording-means could be a pen in contact with a-moving orrotatingchart. In Fig. 2 we have schematically illustrated these features andanyone skilled in the art of'indicating and recording instruments canreadily make the installation. We have indicated by broken line 170 anoperative connection between'modutrol" motor 84 and an indicating and/or recording instrument 171. This instrument can be calibrated todirectly show or iuscribethe'tons (or other weight unit) of concentratepassingthe primary-secondary couple, as previously hereinabovedescribed. Similarly modutrol motor 127 through linkage 172 and recorder173 can show the ratio between concentrate and binder at any time.Finally,'by anelectrical or mechanical linkage 174 effectiveonindicator-recorder 175, the tachometer generator regis- "terstheactual weight of binder being delivered to the conveyor.

What'is claimed is:

1. Apparatus of the character described comprising a source-of afirst'material having magnetic characteristics, a-moving conveyory'afirst feeding means for controlling the flow of said first material fromsaid source onto said conveyor, a first controller effective to'controloperation of said first feeding means, sensing means adjacent saidconveyor and responsive to fluctuations in the magnetic characteristicsof-said first materialcarried on said conveyor, first electric circuitmeans operatively linking said firstcontroller and said sensing meanswhereby to produce,in said first controller, operating fluctuationsresponsive to fluctuations in said sensing means and thereby toachieve'uniformity in the quantity of magnetic material dischargedonsaid conveyor, a source of additional material, a second feeding meansfor controlling the discharge of said additional material onto saidconveyor, a second controller effective to control operation of saidsecond feeding means, a-second electric circuit means operativelylinking said first controller and said second controller whereby tocause said second controller to respond proportionally to the aforesaidfluctuations in said first controller and thereby to cause variations inthe rate of discharge of said additional mater-ialproportionally to anyvariations in the magnetic characteristics of said firs material.

2. Apparatus as defined in elaiml including, in combination therewith, arecorder, and means operatively associating said recorder and said firstcontroller whereby to 'record the amount of magnetic materialpassingsaid sensing-means, said recorder being calibrated to show said lastnamed amount in units of weight.

3. Apparatus as defined in claim 1 includingincombination therewith arecorder operatively associated with saidsecond controller-wherebyto'record the. amount .of additional material delivered by said secondfeeding means, said recorder being calibrated to show said, amountof-said additional material in units of weight.

4. Apparatus-as defined inclaim:l-including, in combinationtherewith,-recording means operatively associated bothwith said firstcontroller and. saidseoond controller and adapted to continuously showthe ratio of delivered magnetic material to delivered additionalmaterial. I

5. Apparatus of the character described for automati- .cally controllingthe feed of an additional, material to a conveyor carrying a magneticmaterial, -;said apparatus comprising means for'moving said conveyorpast a measuring zone, ,sensing means .at ,said lmeasuring.zoneremagnetic'material, and-adapted to transmit a signalproportionally varying with said'variations, a source of magneticmaterial, a first feeding means for feeding magnetic material from saidsource onto said conveyor, a first motor elfective to operate saidfirstfeeding means, a second feeding means for feeding additional materialonto said conveyor, a second motor effective to'operate said secondfeeding'means, a first controller in electrical operative communicationWith said sensing means whereby to receive said varying signal, andeffective upon said first motor to maintain at a constant value the feedof magnetic material, a second controller in electric operativeconnection with said second motor, said first controller being inelectrical communication with said second controller whereby to causesaid second controller to respond to any varying signal from said firstcontroller and thereby to cause feed of said additional material toproportionally vary with feed of magnetic material.

6. Apparatus as defined in claim 5 including, in combination therewith,a quantity recorder, and means operatively associating said recorder andsaid first controller whereby to record the amount of magnetic materialpassing said sensing means, said recorder being calibrated to show saidlast named amount in units of weight.

7. Apparatus as defined in claim 6 including, in combination therewith,a recorder operatively associated with said second controller whereby torecord the amount of additional material delivered by said secondfeeding means, said recorder being calibrated to show said last namedamount in units of weight.

8. Apparatus as defined in claim 1 including, in combination therewithrecording means operatively associated with both said first controllerand said second controller,

and adapted to continuously show the ratio of delivered magneticmaterial to delivered additional material.

9. Apparatus of the character described for automatically controllingthe feed of a binding material to a conveyor carrying a magneticconcentrate material, said apparatus comprising means for moving saidconveyor past a measuring zone, sensing means at said measuring zonecomprising an electrical induction couple responsive to variations inmagnetic characteristics of said magnetic concentrate material, andadapted to transmit an electrical signal proportionally varying withsaid variations in magnetic characteristics, a source of concentrate, afirst feeding-means for-feeding concentrate onto said conveyor, a

jfirst motor effective to operate said first feeding means, a

second feeding'means for feeding binding material onto said conveyor, asecond motor effective to operate said second feeding means, a firstcontroller inelectrical circuit communication with said sensing meanswhereby to be responsive to'said varying signal, a tachometer generatoroperatively connected to said second motor means electrically connectingsaid first controller with said first motor whereby to-impose on saidfirst motor corrective variations responsive to variations in saidvarying signal and thereby to'return to a constant value the concentratefeed, a second controller, means electrically connecting saidsecondcontroller with said first controller whereby to transmit to said secondcontroller a varying signal corresponding to the varying signal fromsaid sensing means to said first controller, and means electricallyconnecting said second controller withsaid second motor and adapted toimpose on said second motor operating variations responsive tovariations in the signal originating in said sensing means'whereby toproduce variations in binder'feed proportional to variations inconcentrate feed.

10. Apparatus as defined in claim 9 including, in combination therewith,a quantity recorder, and means operatively associating said recorder andsaid first controller whereby to record the amount of magneticconcentrate passing said sensing means, said recorder being calibratedto show said last named amount in units of weight.

References Cited in the file of this patent UNITED STATES PATENTS1,727,353 Merrick Sept. 10, 1929 2,428,100 Soulen Sept. 30, 19472,623,658 'Johansen Dec. 30, 1952

